This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Melioidosis is an infectious disease caused by exposure to Burkholderia pseudomallei, a saprophyte found primarily in Southeast Asia and Northern Australia. Melioidosis is considered an emerging infectious disease and epizoonotic agent. Incidence of B. pseudomallei-associated bacterial sepsis and bronchopneumonia has significantly increased in endemic areas over the past decade. B. pseudomallei is a biological threat agent primarily because of its remarkable infectivity at a low (less than 100 bacterial cells) dose. As a result, the Centers of Disease Control and Prevention (CDC) have identified B. pseudomallei as a select biological agent, with a high potential for misuse against masses. Melioidosis is associated with a severe clinical syndrome which is dependant in part on the route of exposure, dose, and immune status of the host, although much remains unclear about pathogenesis of the disease. Although infection from subcutaneous inoculation is not uncommon, inhalation produces the most severe disease. Presently, in vivo study of melioidosis has been mostly restricted to rodent disease models (e.g., hamster, guinea pig). Deciphering the pathogenesis of melioidosis continues to evolve;the role of TLRs in mediating infection and facilitating intracellular entry is of particular importance. We exposed three strains of mice (BALB/c, C57BL/6 or TLR-4 KO transgenics (C3H-Hej)) to aerosolized B. thailandensis to further define the role of Th1-associated host response. Results indicate an increased susceptibility in the C57BL/6 animals, with increased local cytokine response and lethality at lower doses than the TLR-4 KO or BALB/c animals. Dose dependant lung pathology indicated an acute infection in the lungs of the C57BL/6 group compared to signs of chronic infection in the BALB/C mice. TLR-4 KO animals were unaffected by the aerosolized B. thailandensis at the highest doses (1.0E+09 CFU). These results suggest that TLR-4 may not play a prominent role in Burkholderia-related infection, that B. thailandensis can be used as a surrogate agent for experimental laboratory investigation of melioidosis in small animal models, and provides critical information twoard the goal of developing a nonhuman primate model of B. pseudomallei infection.